1. Field of the Invention
The present invention relates to forming silicon comprising films for semiconductor devices and more specifically to forming the silicon comprising films using hexachlorodisilane as a precursor in a single-wafer deposition chamber.
2. Discussion of Related Art
Chemical vapor deposition (CVD) have been widely used to form silicon comprising films such as silicon oxide, silicon nitride, and silicon oxynitride. These films have wide applications in fabrication of integrated circuits such as transistors, microprocessors, and memories. These films are used as spacers, as etch stops, as diffusion and implantation masks, as capacitors, as dielectrics, as anti-reflection coatings, and as final passivation layers. Acceptable processes for making the silicon comprising films include those that form films with uniform thickness, uniform composition, low particulates, low chemical contamination, good adhesion to the substrate, and high throughput for manufacturing.
In a CVD process, given reactant gases such as silane and disilane are introduced into a reaction chamber at particular flow rates. The reactant gases are then decomposed. The intermediate elements from the decomposed gases react together at or near the surface of the heated substrate to form a film (e.g., a silicon oxide film). The gaseous by-products of the reaction are desorbed and removed from the reaction chamber. Energy to drive the reactions can be supplied by several methods, for example by thermal processing, by photons excitation, or by plasma excitation. In a LPCVD (low pressure CVD) process, oxide films are formed using a method and system much like the CVD except the films are formed at a reduced pressure and increased temperature. A conventional CVD or LPCVD system typically contains gas sources, gas feed lines, mass-flow controllers, a reaction chamber, and a heating assembly for heating substrates onto which, the film is deposited.
Silane or disilane chemistry has been widely used as precursors in the CVD or LPCVD processes to make silicon comprising films. With the degree of integration and density of the components to be fabricated onto a semiconductor device, it is important to form the silicon comprising films such as silicon oxide and silicon nitride with good step coverages and good uniformities. As is known, a step coverage refers to the thickness ratio of the film that is formed over the bottom or side to the top of a particular structure (usually a step or a trench) present on a substrate. A good step coverage indicates that this ratio is close to or equal to 1:1. However, with many intricate, dense and complex structures of the components to be formed on the semiconductor device, it is becoming difficult to form uniform films with good step coverage using the current silane and disilane chemistry. Alternative chemistry to the silane and disilane chemistry has been actively sought after. Hexachlorodisilane (Si2Cl6) is one such alternative chemistry. One disadvantage of current methods that utilize the hexachlorodisilane chemistry to form a silicon comprising film includes excessive by-product particle contamination that requires unnecessary and complicated cleaning as well as complicated efficient/exhaust management. Another disadvantage includes slow deposition rate. Further yet, current methods utilize batch processing type of chambers, which limit the rate of customizing and controlling film properties for any particular product.